Self-shielded image guided radiation oncology system

Abstract

An image-guided radiotherapy system adapted to be juxtaposed adjacent a CT scanner comprises a frame having an orifice adapted to permit passage therethrough of a couch on which a patient is positioned, together with a gantry assembly rotatably mounted on the frame in which the gantry assembly comprises a shielding cylinder having an orifice therethrough in alignment with the orifice in the frame. The shielding cylinder has affixed thereto a linac-based treatment head configured to provide radiotherapy, and a beamstop positioned angularly opposite the treatment head to absorb radiation from the treatment head. The shielding cylinder provides sufficient shielding of radiation scattered from the patient and the remainder of the system to not require a conventional vault. In some embodiments an arch may be used instead of a cylinder.

We claim: 
     
       1. An image-guided radiotherapy system not requiring a conventional concrete vault to protect public areas from excessive radiation exposure comprising
 a frame having an orifice adapted to permit passage therethrough of a couch on which a patient is positioned, 
 a gantry assembly rotatably mounted on the frame, the gantry assembly comprising a shielding cylinder having an orifice therethrough in alignment with the orifice in the frame, and 
 the shielding cylinder comprising a shielding arch and having affixed thereto a linac-based, radiation-shielded treatment head configured to provide radiotherapy proximate to an isocenter, and 
 a radiation-shielding beamstop positioned angularly opposite the treatment head to absorb radiation from the treatment head, wherein the radiation shielding provided by the combination of the shielding arch, the treatment head and the beamstop provide sufficient shielding that the radiation emitted during treatment at approximately 6 MeV in doses in a range of approximately 3 Gy/min to approximately 10 Gy/min is less than approximately 300 mrem/year at a distance of at least 3.5 meters from the isocenter. 
 
     
     
       2. The radiotherapy system of  claim 1  wherein the frame is configured to be positioned immediately adjacent a fan beam CT scanner having a couch. 
     
     
       3. The radiotherapy system of  claim 1  wherein the linac-based treatment head provides radiotherapy of approximately 6 MeV energy levels at approximately one meter from the linac. 
     
     
       4. The radiotherapy system of  claim 1  wherein the shielding cylinder places the shielding proximate to the isocenter. 
     
     
       5. The radiotherapy system of  claim 4  wherein the placement of the shielding relative to the isocenter increases the effective dose rate. 
     
     
       6. The radiotherapy system of  claim 5  wherein the treatment head defines a radiation source, and the distance from the radiation source to the isocenter is approximately 85 centimeters with a treatment field of approximately 25 cm by 25 cm at the isocenter. 
     
     
       7. The radiotherapy system of  claim 5  wherein the dose rate at the isocenter is in the range of approximately 3 Gy/min to 6 Gy/min with a field size having a maximum of approximately 25 centimeters by 25 centimeters at the isocenter with an MLC having a leaf width of approximately 10 millimeters and a maximum leaf speed of approximately 3 centimeters per second. 
     
     
       8. The radiotherapy system of  claim 1  wherein the radiation source travels a substantially circular beam path. 
     
     
       9. The radiotherapy system of  claim 1  wherein the treatment head can rotate approximately 270 degrees around the couch and excludes a region below the couch. 
     
     
       10. The radiotherapy system of  claim 1  wherein the treatment head can rotate 360 degrees around the couch. 
     
     
       11. The radiotherapy system of  claim 1  wherein the radiation shielding yielding less than approximately 300 mrem/year at a distance of at least 3.5 meters from the isocenter is achieved without coupling the shielding cylinder, the treatment head and the beamstop. 
     
     
       12. An image-guided radiotherapy (IGRT) system comprising
 a shielding arch configured to block x-ray radiation, and 
 a gantry rotatably mounted to a frame, the gantry having thereon a radiation-shielded linac-based treatment head for delivering radiotherapy proximate to an isocenter and a radiation-shielded beamstop diametrically opposed thereto, with a tunnel passing through both the gantry and the frame configured to receive a couch bearing a patient when the radiotherapy system is juxtaposed adjacent a CT scanner with the tunnel in alignment with a tunnel in the CT scanner, wherein the radiation shielding provided by the combination of the shielding arch, the treatment head and the beamstop provide sufficient shielding that the radiation emitted during treatment at approximately 6 MeV in doses in a range of approximately 3 Gy/min to approximately 10 Gy/min is less than approximately 300 mrem/year at a distance of at least 3.5 meters from the isocenter. 
 
     
     
       13. The radiotherapy system of  claim 12  wherein the beamstop weighs approximately the same as the treatment head. 
     
     
       14. The radiotherapy system of  claim 12  wherein the treatment head can rotate approximately 270 degrees around the couch and excludes a region below the couch. 
     
     
       15. The radiotherapy system of  claim 12  wherein the treatment head can rotate 360 degrees around the couch. 
     
     
       16. The radiotherapy system of  claim 12  further comprising a multileaf collimator (MLC) that provides a leaf size at the isocenter ranging from approximately three millimeters to approximately ten millimeters. 
     
     
       17. The radiotherapy system of  claim 16  configured to provide IGRT with 6 MeV over a twenty-five centimeter field with a ten millimeter MLC. 
     
     
       18. The image-guided radiotherapy system of  claim 1  wherein the shielding cylinder and the beamstop combine to provide shielding of approximately five Tenth-Value-Layers. 
     
     
       19. A vaultless image-guided radiotherapy system comprising
 a frame having an orifice therethrough adapted to permit passage of a couch on which a patient is positioned, 
 a gantry assembly rotatably mounted on the frame, the gantry assembly comprising a shielding cylinder having a tunnel therethrough in alignment with the orifice in the frame, and 
 the shielding cylinder having affixed thereto a linac-based, radiation-shielded treatment head configured to provide radiotherapy, and a beamstop positioned angularly opposite the treatment head to absorb radiation from the treatment head, wherein the shielding cylinder is comprised of steel and the beamstop is comprised of lead in sufficient thickness that the combination of the shielding cylinder, radiation-shielded treatment head and beamstop cooperate to shield radiation from the treatment head such that radiation along a longitudinal (patient) axis at approximately 2.8 meters from an isocenter defined by the treatment head is reduced to approximately 3.6 mR/hr. 
 
     
     
       20. The vaultless image-guided radiotherapy system of  claim 19  wherein leakage radiation is no more than approximately 0.005 percent of the exposure rate at the isocenter.